Is it generally possible to send requests to specific, individual rails
server processes? From within the walls, that is, not externally.

My concrete purpose is to clear caches of data loaded from the database
without having to restart the server process.

With the common Mongrel (et al.) + load balancer setup, each server
process has its own port and presumably the relevant information is
accessible from the deployment specification. I have no idea how things
are with passenger.

I’m not sure if this is what you are looking for, but if I need to
send a request directly to a specific Mongrel/Thin instance (bypassing
the load balancer), I just call it like: http://mongrel/thin-server:8000
(or whatever port you need)

I’m not sure if this is what you are looking for, but if I need to
send a request directly to a specific Mongrel/Thin instance
(bypassing the load balancer), I just call it like:http://mongrel/thin-server:8000 (or whatever port you need)

Yes, with Mongrel and similarly load-balanced servers this works. But
how about Passenger?